Nearest vertex

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Find the closest vertex and coordinate of a geometry to a point.

screenshot

Use case

Determine the shortest distance between a location and the boundary of an area. For example, developers can snap imprecise user clicks to a geometry if the click is within a certain distance of the geometry.

How to use the sample

Click anywhere on the map. A yellow cross will show at that location. A blue circle will show the polygon's nearest vertex to the point that was clicked. A red diamond will appear at the coordinate on the geometry that is nearest to the point that was clicked. If clicked inside the geometry, the red and orange markers will overlap. The information box showing distance between the clicked point and the nearest vertex/coordinate will be updated with every new location clicked.

How it works

  1. Get a Geometry and a Point to check the nearest vertex against.
  2. Call GeometryEngine::nearestVertex(inputGeometry, point).
  3. Use the returned ProximityResult to get the Point representing the polygon vertex, and to determine the distance between that vertex and the clicked point.
  4. Call GeometryEngine::nearestCoordinate(inputGeometry, point).
  5. Use the returned ProximityResult to get the Point representing the coordinate on the polygon, and to determine the distance between that coordinate and the clicked point.

Relevant API

  • GeometryEngine
  • ProximityResult

Tags

analysis, coordinate, geometry, nearest, proximity, vertex

Sample Code

NearestVertex.cppNearestVertex.cppNearestVertex.hNearestVertex.qml
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// [WriteFile Name=NearestVertex, Category=Geometry]
// [Legal]
// Copyright 2020 Esri.

// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
// http://www.apache.org/licenses/LICENSE-2.0

// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// [Legal]

#ifdef PCH_BUILD
#include "pch.hpp"
#endif // PCH_BUILD

#include "NearestVertex.h"

#include "GeometryEngine.h"
#include "Graphic.h"
#include "GraphicsOverlay.h"
#include "Map.h"
#include "MapQuickView.h"
#include "PolygonBuilder.h"
#include "SimpleFillSymbol.h"
#include "SimpleLineSymbol.h"
#include "SimpleMarkerSymbol.h"

using namespace Esri::ArcGISRuntime;

NearestVertex::NearestVertex(QObject* parent /* = nullptr */):
  QObject(parent),
  m_map(new Map(BasemapStyle::ArcGISTopographic, this))
{
  const Point center(-4487263.495911, 3699176.480377, SpatialReference::webMercator());
  const Viewpoint viewpoint(center, 80000000);
  m_map->setInitialViewpoint(viewpoint);
}

NearestVertex::~NearestVertex() = default;

void NearestVertex::init()
{
  // Register the map view for QML
  qmlRegisterType<MapQuickView>("Esri.Samples", 1, 0, "MapView");
  qmlRegisterType<NearestVertex>("Esri.Samples", 1, 0, "NearestVertexSample");
}

MapQuickView* NearestVertex::mapView() const
{
  return m_mapView;
}

int NearestVertex::vertexDistance() const
{
  return m_vertexDistance;
}

int NearestVertex::coordinateDistance() const
{
  return m_coordinateDistance;
}

// Set the view (created in QML)
void NearestVertex::setMapView(MapQuickView* mapView)
{
  if (!mapView || mapView == m_mapView)
    return;

  m_mapView = mapView;
  m_mapView->setMap(m_map);

  // shows the polygon, clicked location, and nearest coordinate and vertex on polygon
  setupGraphics();

  emit mapViewChanged();
}

void NearestVertex::setupGraphics()
{
  // create a graphics overlay to show the polygon, clicked location, and nearest vertex
  GraphicsOverlay* graphicsOverlay = new GraphicsOverlay(this);

  // Points for polygon in the middle of Atlantic Ocean
  QList<Point> points = {
    Point(-5991501.677830, 5599295.131468),
    Point(-6928550.398185, 2087936.739807),
    Point(-3149463.800709, 1840803.011362),
    Point(-1563689.043184, 3714900.452072),
    Point(-3180355.516764, 5619889.608838)
  };

  PolygonBuilder* polygonBuilder = new PolygonBuilder(SpatialReference::webMercator(), this);
  polygonBuilder->addPoints(points);
  SimpleLineSymbol* polygonOutlineSymbol = new SimpleLineSymbol(SimpleLineSymbolStyle::Solid, Qt::green, 2, this);
  SimpleFillSymbol* polygonFillSymbol = new SimpleFillSymbol(SimpleFillSymbolStyle::ForwardDiagonal, Qt::green, polygonOutlineSymbol, this);
  Graphic* polygonGraphic = new Graphic(polygonBuilder->toGeometry(), polygonFillSymbol, this);

  graphicsOverlay->graphics()->append(polygonGraphic);

  // create graphics for the clicked location, nearest coordinate, and nearest vertex markers
  SimpleMarkerSymbol* clickedLocationSymbol = new SimpleMarkerSymbol(SimpleMarkerSymbolStyle::X, Qt::yellow, 15, this);
  SimpleMarkerSymbol* nearestCoordinateSymbol = new SimpleMarkerSymbol(SimpleMarkerSymbolStyle::Diamond, Qt::red, 10, this);
  SimpleMarkerSymbol* nearestVertexSymbol = new SimpleMarkerSymbol(SimpleMarkerSymbolStyle::Circle, Qt::blue, 15, this);

  Graphic* clickedLocationGraphic = new Graphic(this);
  clickedLocationGraphic->setSymbol(clickedLocationSymbol);
  Graphic* nearestCoordinateGraphic = new Graphic(this);
  nearestCoordinateGraphic->setSymbol(nearestCoordinateSymbol);
  Graphic* nearestVertexGraphic = new Graphic(this);
  nearestVertexGraphic->setSymbol(nearestVertexSymbol);

  graphicsOverlay->graphics()->append(clickedLocationGraphic);
  graphicsOverlay->graphics()->append(nearestCoordinateGraphic);
  graphicsOverlay->graphics()->append(nearestVertexGraphic);

  // add graphic to clicked location
  connect(m_mapView, &MapQuickView::mouseClicked, this,
          [nearestVertexGraphic, nearestCoordinateGraphic, polygonBuilder, clickedLocationGraphic, this]
          (QMouseEvent& e)
  {
    const Point clickedLocation = m_mapView->screenToLocation(e.x(), e.y());
    // normalizing the geometry before performing geometric operations
    const Geometry normalizedPoint = GeometryEngine::normalizeCentralMeridian(clickedLocation);

    clickedLocationGraphic->setGeometry(normalizedPoint);

    const ProximityResult nearestCoordinateResult = GeometryEngine::nearestCoordinate(polygonBuilder->toGeometry(), normalizedPoint);
    nearestCoordinateGraphic->setGeometry(nearestCoordinateResult.coordinate());

    const ProximityResult nearestVertexResult = GeometryEngine::nearestVertex(polygonBuilder->toGeometry(), normalizedPoint);
    nearestVertexGraphic->setGeometry(nearestVertexResult.coordinate());

    // get distance in kilometers
    m_vertexDistance = nearestVertexResult.distance()/1000;
    m_coordinateDistance = nearestCoordinateResult.distance()/1000;

    e.accept();
    emit vertexDistanceCalculated();
    emit coordinateDistanceCalculated();
  });

  m_mapView->graphicsOverlays()->append(graphicsOverlay);
}

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